Problem loading font preloads with query cache bust parameter

Found out that even with fixes for type there were additional problem in CSS rules that are probably coming from core CSS aggregator - there URL was still wrong and it had additional `=` sign which produced two font URLS that needed to be fetched - one preloaded and one regular. So I decided to add a `v` as a key for query parameter for font icon cache bust which will now look like:

preload-fonts:
  - 'fonts/icons.woff2?v=2'

Anyway this makes more sense and it is fixing all problems that we can have with core when we are using query parameter without a key.

I've also updated relative documentations in https://www.drupal.org/docs/8/themes/bs-base/additional-features/icons-f... → and https://www.drupal.org/docs/8/themes/bs-base/additional-features/fonts-p... → with more notes about this issue.

Committed.

Automatically closed - issue fixed for 2 weeks with no activity.